Multilayer ceramic capacitor

ABSTRACT

A multilayer ceramic capacitor includes a laminated body and first and second external electrodes respectively on both end surfaces of the laminated body. When regions where first internal electrodes or second internal electrodes are not present are regarded as side margin portions in a cross section of the laminated body as viewed from the laminating direction, the side margin portions include multiple side margin layers, and the content of Si in the side margin layer closest to the internal electrode is lower than that in the side margin layer other than the side margin layer closest to the internal electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication 2015-142975 filed Jul. 17, 2015, the entire contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a multilayer ceramic capacitor.

2. Description of the Related Art

In recent years, multilayer ceramic capacitors have been required whichare high in capacitance and small in size. Such multilayer ceramiccapacitors each have a laminated body formed in a rectangular orsubstantially rectangular parallelepiped shape, for example, wheredielectric layers for inner layers with internal electrodes printed andthe internal electrodes are laminated alternately, and furthermore,ceramic layers for outer layers are laminated on the upper surface andlower surface thereof. Further, the capacitors each have externalelectrodes formed on both end surfaces of the laminated body.

Some of the multilayer ceramic capacitors have dielectric layersreferred to as side margin portions, which are formed on side surfacesof the laminated bodies for preventing the internal electrodes frombeing connected to the external electrodes at the side surfaces.

JP 61-248413 A discloses a method for manufacturing a multilayer ceramiccapacitor including such side margin portions as described previously.In the method for manufacturing a multilayer ceramic capacitor asdescribed in JP 61-248413 A, first, ceramic green sheets are stackedwhich have, on the surfaces thereof, conductive films formed to defineand function as internal electrodes. Next, a mother stacked body isformed, and cut such that the conductive films are exposed at sidesurfaces with no external electrodes formed in cutting the motherstacked body. As a result, a stacked body chip is obtained. Then,ceramic slurry to define and function as the side margin portions isapplied to the internal electrodes exposed at both sides of the cutstacked body chip. Thus, it becomes possible to form the internalelectrodes over the entire width of the stacked body chip, thus makingit possible to increase the efficiency of acquiring the electrostaticcapacitance, and to reduce the fluctuation in electrostatic capacitance.

However, the multilayer ceramic capacitor in JP 61-248413 A fails toachieve sufficient strength for the side margin portions, for example,when the thicknesses of the side margin portions, that is, the dimensionof the stacked body in the width direction is reduced for the purpose ofachieving higher capacitance in a smaller size of multilayer ceramiccapacitor. Thus, the multilayer ceramic capacitor in JP 61-248413 A hasthe problem of failing to achieve sufficient deflecting strength.Moreover, the side margin portions are made more likely to be cracked orchipped, and ingress of water is caused from the cracks or chips. Thus,the multilayer ceramic capacitor in JP 61-248413 A has the problem ofdecreased insulation properties.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a multilayerceramic capacitor which has improved reliability achieved by improving astrength of side margin portions even when the side margin portions havea small dimension in a width direction.

A multilayer ceramic capacitor according to a preferred embodiment ofthe present invention includes a laminated body including a plurality ofdielectric layers laminated and a plurality of internal electrodes; andexternal electrodes electrically connected to the internal electrodes,wherein the laminated body preferably has a rectangular or substantiallyrectangular parallelepiped shape including a first principal surface anda second principal surface opposed in the laminating direction, a firstside surface and a second side surface opposed in the width directionperpendicular or substantially perpendicular to the laminatingdirection, and a first end surface and a second end surface opposed inthe length direction perpendicular or substantially perpendicular toboth the laminating direction and the width direction, the plurality ofinternal electrodes includes first internal electrodes exposed at thefirst end surface, and second internal electrodes exposed at the secondend surface to be opposed to the first internal electrodes with thedielectric layers interposed therebetween, the plurality of externalelectrodes includes a first external electrode that covers the first endsurface and is electrically connected to the first internal electrodes,and a second external electrode that covers the second end surface andis connected to the second internal electrodes, and when regions wherethe first internal electrodes or the second internal electrodes are notpresent are regarded as side margin portions in a cross section of thelaminated body as viewed from the laminating direction, the side marginportions include multiple side margin layers, and the content of Si inthe side margin layer closest to the internal electrode is lower thanthat in the side margin layer other than the side margin layer closestto the internal electrode.

In addition, in a multilayer ceramic capacitor according to a preferredembodiment of the present invention, exposed surfaces of the firstinternal electrodes and the second internal electrodes at the first sidesurface of the laminated body and the second side surface thereofpreferably contain more Si than central portions of the first internalelectrodes and the second internal electrodes.

Furthermore, in a multilayer ceramic capacitor according to a preferredembodiment of the present invention, the side margin portions preferablyhave Si mole number/Ti mole number of about 1.0 or more and about 7.0 orless.

Furthermore, in a multilayer ceramic capacitor according to a preferredembodiment of the present invention, the side margin portions preferablyhave a dimension of about 5 μm or more and about 40 μm or less in thewidth direction.

In a multilayer ceramic capacitor according to a preferred embodiment ofthe present invention, when regions where the first internal electrodesor the second internal electrodes are not present are regarded as theside margin portions in the laminated body as viewed from the laminatingdirection, the side margin portions have multiple side margin layers,and the content of Si in the side margin layer closest to the internalelectrode is lower than that in the side margin layer other than theside margin layer closest to the internal electrode. Thus, the strengthof the side margin portions is increased. Thus, the deflecting strengthof the multilayer ceramic capacitor is improved. Furthermore, the sidemargin portions are made less likely to be cracked or chipped, andingress of water is thus able to be prevented. Thus, insulatingproperties of the multilayer ceramic capacitor are able to be ensured.As a result, the multilayer ceramic capacitor achieves sufficientreliability.

According to various preferred embodiments of the present invention, amultilayer ceramic capacitor achieves improved reliability by improvingthe strength of side margin portions even when the side margin portionshave a small dimension in the width direction.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an appearance perspective view of a multilayer ceramiccapacitor according to a preferred embodiment of the present invention.

FIG. 2 is a cross-sectional view along the line A-A of FIG. 1, whichillustrates a multilayer ceramic capacitor according to a preferredembodiment of the present invention.

FIG. 3 is a cross-sectional view along the line B-B of FIG. 1, whichillustrates a multilayer ceramic capacitor according to a preferredembodiment of the present invention.

FIG. 4 is an enlarged view of a portion C in FIG. 3, which illustrates amultilayer ceramic capacitor according to a preferred embodiment of thepresent invention.

FIG. 5 is a diagram of an image taken by WDX, of Si segregation portionsof a side margin portion included in the multilayer ceramic capacitoraccording to a multilayer ceramic capacitor according to a preferredembodiment of the present invention.

FIG. 6 is a diagram of an image taken by a WDS, of Mg segregationportions in the vicinity of the surface of a side margin portionincluded in the multilayer ceramic capacitor according to a preferredembodiment of the present invention.

FIG. 7 is a diagram of an image taken by a WDS, of Ni segregationportions in the vicinity of the surface of a side margin portionincluded in a preferred embodiment of the present invention.

FIG. 8 is a diagram of an image taken by a WDS, of Si segregationportions in the vicinity of the surface of a side margin portionincluded in a preferred embodiment of the present invention.

FIGS. 9A and 9B are diagrams for explaining a method for manufacturing amultilayer ceramic capacitor according to a preferred embodiment of thepresent invention, where FIG. 9A is a schematic view illustratingceramic green sheets with conductive films formed, and FIG. 9B is apattern diagram illustrating the stacked ceramic green sheets with theconductive films formed.

FIG. 10 is a perspective view illustrating an example of the appearanceof a laminated body chip obtained by the method for manufacturing amultilayer ceramic capacitor according to a preferred embodiment of thepresent invention.

FIG. 11 is a diagram showing the relationship between the pore arearatio in the vicinity of the side margin portion surface and the Vickershardness at the side margin portion surface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A multilayer ceramic capacitor according to a preferred embodiment ofthe present invention will be described with reference to FIGS. 1 to 4.FIG. 1 is an appearance perspective view illustrating a multilayerceramic capacitor according to a preferred embodiment of the presentinvention. FIG. 2 is a cross-sectional view along the line A-A of FIG.1, which illustrates the multilayer ceramic capacitor according to apreferred embodiment of the present invention. FIG. 3 is across-sectional view along the line B-B of FIG. 1, which illustrates themultilayer ceramic capacitor according to a preferred embodiment of thepresent invention. FIG. 4 is an enlarged view of a portion C in FIG. 3,which illustrates the multilayer ceramic capacitor according to apreferred embodiment of the present invention.

As shown in FIG. 1, the multilayer ceramic capacitor 10 according tothis preferred embodiment preferably includes a laminated body 12, andfirst and second external electrodes 40, 42 provided respectively onboth end surfaces of the laminated body 12.

Example sizes of the multilayer ceramic capacitor 10 according to apreferred embodiment of the present invention include approximate sizessuch as, for example, “1.6 mm×0.8 mm×0.8 mm”, “1.0 mm×0.5 mm×0.5 mm”,“0.6 mm×0.3 mm×0.3 mm”, “0.4 mm×0.2 mm×0.2 mm”, or “0.2 mm×0.1 mm×0.1mm”, when the size is expressed as “the dimension in the length (L)direction X the dimension in the width (W) direction X the dimension inthe laminating (T) direction”.

As shown in FIG. 1, the laminated body 12 preferably has a rectangularor substantially rectangular parallelepiped shape. The laminated body 12includes a first end surface 13 and a second end surface 14 extending inthe width (W) direction and the laminating (T) direction, a first sidesurface 15 and a second side surface 16, extending in the length (L)direction and the laminating (T) direction, and a first principalsurface 17 and a second principal surface 18 extending in the length (L)direction and the width (W) direction. The first end surface 13 and thesecond end surface 14 are opposed to each other, the first side surface15 and the second side surface 16 are opposed to each other, and thefirst principal surface 17 and the second principal surface 18 areopposed to each other. In addition, the first side surface 15 and thesecond side surface 16 are perpendicular or substantially perpendicularto the first end surface 13 and the second end surface 14, and the firstprincipal surface 17 and the second principal surface 18 areperpendicular or substantially perpendicular to the first end surface 13and the first side surface 15. Further, as long as the laminated body 12has a rectangular or substantially rectangular parallelepiped shape,corners and ridges thereof are preferably rounded or the like.

As shown in FIG. 2, the laminated body 12 includes first internalelectrodes 22 provided at the interfaces between ceramic layers 20defining inner layers, and second internal electrodes 24 opposed to thefirst internal electrodes 22 with the ceramic layers 20 interposedtherebetween. The multiple combinations of the ceramic layers 20, firstinternal electrodes 22, and second internal electrodes 24 are stacked todefine an inner layer portion 26. An outer layer portion 28 and an outerlayer portion 30 sandwich the inner layer portion 26 from the laminating(T) direction. The outer layer portion 28 include a plurality of ceramiclayers 46 defining outer layers, whereas the outer layer portion 30includes a plurality of ceramic layers 48 defining outer layers. Sidemargin portions 32 and 34 sandwich the inner layer portion 26 and theouter layer portions 28, 30 from the width (W) direction. The sidemargin portions 32 and 34 include multiple ceramic layers defining sidemargins. In other words, the inner layer portion 26 is a regionsandwiched between the first internal electrode 22 b closest to thefirst principal surface 17 and the second internal electrode 24 bclosest to the second principal surface 18 in the laminating (T)direction. In addition, the side margin portions 32, 34 are regionswhere the first internal electrodes 22 and the second internalelectrodes 24 are not present in a cross section of the laminated body12 as viewed from the laminating (T) direction.

The multiple ceramic layers 20 defining inner layers are each sandwichedbetween the first internal electrode 22 and the second internalelectrode 24. The ceramic layers 20 defining inner layers are composedof, for example, dielectric ceramic grains that contain, as their mainconstituent, a perovskite-type compound containing Ba and Ti, and have aperovskite structure. In addition to their main constituent, at leastone of Si, Mg, and Ba may be added as an additive. The additive ispresent between the ceramic grains. The fired ceramic layers 20 defininginner layers preferably are about 0.2 μm or more and about 10 μm or lessin thickness, for example.

For the laminated body 12, the ceramic layers 46, 48 defining the outerlayer portions 28, 30 provided at the top and bottom of the body, arepreferably made from the same dielectric ceramic material as the ceramiclayers 20 defining inner layers. It is to be noted that the ceramiclayers 46, 48 defining outer layers may be made of a material that isdifferent from the ceramic layers 20 defining inner layers. In addition,when the ceramic layers 46, 48 defining outer layers each have amultilayer structure, as compared with Si segregation portions of theceramic layers 46, 48 defining outer layers, located closest to thefirst and second internal electrodes 22 b, 24 b, the other ceramiclayers 46, 48 defining outer layers preferably have more segregationportions. Thus, the deflecting strength is improved from the laminating(T) direction of the multilayer ceramic capacitor 10. It is to be notedthat the fired outer layer portions 28, 30 preferably are about 15 μm ormore and about 40 μm or less in thickness, for example. Further, theceramic layers 46, 48 defining outer layers may each have a single-layerstructure, rather than a multilayer structure.

The first internal electrodes 22 and the second internal electrodes 24are opposed with the ceramic layers 20 defining inner layers interposedtherebetween in the laminating (T) direction. Electrostatic capacitanceis generated by the portions where the first internal electrodes 22 andthe second internal electrodes 24 are opposed with the ceramic layers 20defining inner layers interposed therebetween.

The ceramic layers 20 defining inner layers extend in the width (W)direction and the length (L) direction, and the multiple first internalelectrodes 22 each extend in the form of a plate along the ceramiclayers 20 defining inner layers. The multiple first internal electrodes22 are each extended to the first end surface 13 of the laminated body12, and electrically connected to the first external electrode 40. Inaddition, the multiple second internal electrodes 24 each extend in theform of a plate to be opposed to the first internal electrodes 22 withthe ceramic layers 20 defining inner layers interposed therebetween.

The multiple second internal electrodes 24 are each extended to thesecond end surface 14 of the laminated body 12, and electricallyconnected to the second external electrode 42.

The first and second internal electrodes 22, 24 preferably are each, forexample, about 0.3 μm or more and about 2.0 μm or less in thickness. Thefirst and second internal electrodes 22, 24 preferably contain Ni.

It is to be noted that the electrodes can contain, besides Ni, metalssuch as Cu, Ag, Pd, an Ag—Pd alloy, and Au, for example. Further, thefirst and second internal electrodes 22, 24 may include the samedielectric grains as the ceramic layers 20 defining inner layers.

As shown in FIG. 4, Si is segregated at sites of the first and secondinternal electrodes 22, 24, including surfaces exposed most to the sidemargin portions 32, 34. The Si has segregation regions in the internalelectrode domain at least within a range of about 0.5 μm or less fromthe side margin portions toward a central portion in the width (W)direction, and forms segregation portions 22 a, 24 a. In other words,the segregation portions 22 a are provided at the first internalelectrodes 22 close to the side margin portions 32, 34, whereas thesegregation portions 24 a are provided at the second internal electrodesclose to the side margin portions 32, 34.

The segregation portions 22 a, 24 a improve the deflecting strength ofthe multilayer ceramic capacitor 10.

When the regions where the first internal electrodes 22 or the secondinternal electrodes 24 are not present are regarded as the side marginportions 32, 34 in a cross section of the laminated body 12 as viewedfrom the laminating (T) direction, the side margin portions 32, 34 havemultiple side margin layers, the content of Si in the side margin layersclosest to the internal electrodes 22, 24 is lower than that in theother side margin layers, and thus the strength of the side marginportions 32, 34 can be increased. Thus, the deflecting strength of themultilayer ceramic capacitor 10 is improved. Furthermore, the sidemargin portions 32, 34 are made less likely to be cracked or chipped,and ingress of water is thus prevented. Thus, insulation properties ofthe multilayer ceramic capacitor 10 are able to be ensured. As a result,the multilayer ceramic capacitor 10 achieves sufficient reliability.

In addition, the deflecting strength of the multilayer ceramic capacitor10 is able to be further improved when the first internal electrodes 22and second internal electrodes 24 of the laminated body 12 includes thesegregation portions 22 a, 24 a close to the side margin portions 32,34, with the segregation portions 22 a, 24 a containing Si. The sidemargin portions 32, 34 each have a multilayer structure including outerlayers 32 a, 34 a located close to the first and second side surfaces15, 16 of the laminated body 12, and inner layers 32 b, 34 b locatedclose to the first and second internal electrodes 22, 24. It is to benoted that the multilayer structures of the side margin portions 32, 34can be easily confirmed by observing the difference in sinterabilitybetween the outer layers 32 a, 34 a and the inner layers 32 b, 34 b withthe use of an optical microscope.

The dimensions of the fired side margin portions 32, 34 in the width (W)direction are, for example, 5 μm or more and 40 μm or less. Morepreferably, the dimensions are 20 μm or less. In addition, thedimensions of the outer layers 32 a, 34 a in the width (W) direction arelarger than the dimensions of the inner layers 32 b, 34 b in the width(W) direction. Specifically, the dimensions of the outer layers 32 a, 34a in the width (W) direction are 5 μm or more and 20 μm or less. Thedimensions of the inner layers 32 b, 34 b in the width (W) direction are0.1 μm or more and 20 μm or less.

It is to be noted that the dimensions of the side margin portions 32, 34in the width (W) direction in the invention mean average dimensionscalculated from the result of measuring, at multiple points, thedimensions of the side margin portions 32, 34 in the laminating (T)direction. The measurement method is as follows. First, a surface(hereinafter, referred to as a “WT cross section”) of the multilayerceramic capacitor 10 is exposed which includes the width (W) directionand the laminating (T) direction. Next, images of the WT cross sectionare taken with an optical microscope such that ends of the first andsecond internal electrodes 22, 24 in the width (W) direction and one ofthe side margin portions 32, 34 are included in the same field of view.As for the imaging points, three points of upper, central, and lowerparts are each imaged in the laminating (T) direction. Then, in each ofthe upper, central, and lower parts, multiple line segments parallel tothe width (W) direction are drawn from the ends of the first and secondinternal electrodes 22, 24 in the width (W) direction toward the firstand second side surfaces 15, 16, and the length of each line segment ismeasured. The average value for the lengths of the line segmentsmeasured as just described is calculated in each of upper, central, andlower parts. In addition, the respective average values are furtheraveraged, thus providing the thickness dimensions of the side marginportions 32, 34.

The side margin portions 32, 34 are composed of, for example, adielectric ceramic material including a perovskite structure composed ofa main constituent such as BaTiO₃. Si is added as an additive to themain constituent, and between ceramic grains there are portions wherethe additive is segregated. The presence of the Si segregation portionsimproves the deflecting strength of the side margin portions 32, 34. Siis added to the outer layers 32 a, 34 a at the Si mole number/Ti molenumber of 3.0 or more and 7.0 or less, and added to the inner layers 32b, 34 b at the Si mole number/Ti mole number of 1.0 or more and 4.0 orless. In particular, there are more Si segregation portions in the outerlayers 32 a, 34 a than in the inner layers 32 b, 34 b.

FIG. 5 is a diagram of an image taken by a wavelength dispersive X-rayspectrometer (hereinafter, referred to as WDX), of Si segregationportions of the side margin portion included in the multilayer ceramiccapacitor 10. The Si segregation portions of the side margin portions32, 34 can be confirmed by exposing a WT cross section substantially inthe center of the laminated body 12 in the length (L) direction, andthen observing the section with the use of a WDX. Furthermore, it can beconfirmed that the Si segregation portions 22 a, 24 a are formed at thefirst and second internal electrodes 22, 24 closest to the side marginportions 32, 34. It is to be noted that the segregation of not only Sibut also Mg is also confirmed. FIGS. 6 to 8 are diagrams of images takeby a WDS, of the same site (in the vicinity near the surface of the sidemargin portion) of the multilayer ceramic capacitor 10, where FIG. 6 isa diagram of an image of a Mg segregation portion, FIG. 7 is a diagramof an image of a Ni segregation portion, and FIG. 8 is a diagram of animage of an Si segregation portion.

The amounts of Ba as an additive between ceramic grains for each of theceramic layers 20 defining inner layers, the outer layers 32 a, 34 a,and the inner layers 32 b, 34 b are: ceramic layers for inner layers20<outer layers 32 a, 34 a<inner layers 32 b, 34 b.

As just described, the content of Ba between ceramic grains varies witheach of the ceramic layers 20 defining inner layers, the outer layers 32a, 34 a, and the inner layers 32 b, 34 b. It is to be noted that thedifferences in Ba content can be found by TEM analysis.

In addition, the contents of Ba in the inner layer portion 26 and theouter layers 32 a, 34 a and inner layers 32 b 34 b of the side marginportions 32, 34 are prepared such that in terms of molar ratio as acenter value with respect to 1 mol of Ti, the outer layers 32 a, 34 a ishigher than 1.01 and 1.020 or lower; the inner layers 32 b, 34 n arehigher than 1.020 and lower than 1.040; and the inner layer portion 26is higher than 0.99 and lower than 1.01.

Here is a method for confirming the molar ratios mentioned above. First,the outer layers 32 a, 34 a, and inner layers 32 b, 34 b in the sidemargin portions 32, 34 of the laminated body 12 are polished from theside margin portions 32, 34. Next, the powders of the outer layers 32 a,34 a and inner layers 32 b, 34 b, which are obtained by the polishing,are each dissolved with an acid. Then, ICP emission spectrometry canconfirm whether the outer layers 32 a, 34 a and the inner layers 32 b,34 b have the molar ratios mentioned above.

The content of Ba added between ceramic grains of the inner layers 32 b,34 b is higher in the range in excess of 100% and less than 140% withrespect to the content of Ba between ceramic grains of the outer layers32 a, 34 a.

In addition, the side margin portions 32, 34 are formed such that voidportions are reduced from the internal electrode side toward the sidesurface side. More specifically, there are fewer void portions in theouter layers 32 a, 34 a than in the inner layers 32 b, 34 b. Thus,ingress of water is suppressed from the side margin portions 32, 34 intothe laminated body 12, and the moisture resistance of the multilayerceramic capacitor 10 can be thus improved. Furthermore, insulationproperties of the multilayer ceramic capacitor 10 can be ensured.

The first external electrode 40 is covers the first end surface 13 ofthe laminated body 12, and is electrically connected to the firstinternal electrode 22 extended to the first end surface 13 of thelaminated body 12. In addition, the second external electrode 42 coversthe second end surface 14 of the laminated body 12, and is electricallyconnected to the second internal electrode 24 extended to the second endsurface 14 of the laminated body 12.

As shown in FIGS. 1 and 2, the first external electrode 40 has athree-layer structure including a base electrode layer 40 a, lower-layerplating 40 b formed on the surface of the base electrode layer 40 a, andupper layer plating 40 c formed on the surface of the lower-layerplating 40 b. The base electrode layer 40 a is provided to entirelycover the first end surface 13 of the laminated body 12, and alsoprovided to cover, from the portion Covering the end surface 13,portions of the respective first side surface 15 and second side surface16 as well as portions of the respective first principal surface 17 andsecond principal surface 18.

As shown in FIGS. 1 and 2, the second external electrode 42 has athree-layer structure including a base electrode layer 42 a, lower-layerplating 42 b formed on the surface of the base electrode layer 42 a, andupper layer plating 42 c formed on the surface of the lower-layerplating 42 b. The base electrode layer 42 a is provided to entirelycover the second end surface 14 of the laminated body 12, and alsoprovided to cover, from the portion Covering the end surface 14,portions of the respective first side surface 15 and second side surface16 as well as portions of the respective first principal surface 17 andsecond principal surface 18.

The base electrode layers 40 a, 42 a preferably contains Cu formed bybaking.

Further, the layers may contain, for example, Ni, Ag, Pd, a Ag—Pd alloy,or Au, besides Cu. In addition, the base electrode layers 40 a, 42 a mayhave multiple layers. It is to be noted that the base electrode layers40 a, 42 a may be formed by firing simultaneously with the firstinternal electrodes 22 and the second internal electrodes 24, so-calledco-firing, or formed by applying and baking a conductive paste,so-called post-firing. Alternatively, the base electrode layers 40 a, 42a may be formed directly by plating, or formed by curing a resin layerincluding conductive grains and a thermosetting resin.

The lower layer platings 40 b, 42 b preferably contain Ni for preventingsolder leaching. In addition, the upper layer platings 40 c, 42 cpreferably contain Sn for enhancing mountability. Further, the lowerlayer platings 40 b, 42 b can contain, besides Ni, or the upper layerplatings 40 c, 42 c can contain, besides Sn, for example, Cu, Ag, Pd, anAg—Pd alloy, or Au. Further, a conductive resin layer for stressrelaxation may be formed between the base electrode layer 40 a and thelower layer plating 40 b and between the base electrode layer 42 a andthe lower layer plating 42 b. Alternatively, through plating directlyonto the laminated body 12, the first and second external electrodes 40,42 may be formed by the plating.

It is to be noted that in the case of direct plating as the externalelectrodes 40, 42, and in the case of using Ni as the first and secondinternal electrodes 22, 24, it is preferable to use, as the lower layerplatings 40 b, 42 b, Cu which is favorably joined with Ni. Furthermore,the upper layer platings 40 c, 42 c preferably have two-layer structuresincluding first upper plating layers formed on the surfaces of the lowerlayer platings 40 b, 42 b, and second upper plating layers formed on thesurfaces of the first upper plating layers. The first upper platinglayers preferably contain Ni that has the function of preventing solderleaching. The second upper plating layers preferably contain Sn or Authat has favorable solderability.

As shown in FIG. 3, the side margin portions 32, 34 of the multilayerceramic capacitor 10 according to this preferred embodiment preferablyinclude multiple layers. The side margin portion 32 includes the outerlayer 32 a and the inner layer 32 b. The inner layer 32 b is disposedbetween the first and second internal electrodes 22, 24 and the outerlayer 32 a. The content of Si in the outer layer 32 a which is a sidemargin layer other than the inner layer 32 b is higher than that in theinner layer 32 b disposed closest to the first and second internalelectrodes 22, 24. The side margin portion 34 includes the outer layer34 a and the inner layer 34 b. The inner layer 34 b is disposed betweenthe first and second internal electrodes 22, 24 and the outer layer. Thecontent of Si in the outer layer 34 a which is a side margin layer otherthan the inner layer 34 b is higher than that in the inner layer 34 bdisposed closest to the first and second internal electrodes 22, 24.Thus, the strength of the side margin portions 32, 34 is improved, andthe deflecting strength of the multilayer ceramic capacitor 10 is thusimproved. Furthermore, the side margin portions 32, 34 are made lesslikely to be cracked or chipped, ingress of water is thus prevented, andinsulation properties of the multilayer ceramic capacitor 10 are thusensured. As a result, the multilayer ceramic capacitor 10 is able to beprovided which reliability improved reliability. In addition, there areinterfaces between the outer layers 32 a, 34 a and the inner layers 32b, 34 b, and these interfaces relax stress applied onto the multilayerceramic capacitor 10.

In addition, in the multilayer ceramic capacitor 10 according to thispreferred embodiment, the surfaces closest to the side margin portions32, 34 contain more Si than central portions of the first and secondinternal electrodes 22, 24. As a result, the strength of the side marginportions 32, 34 is further improved.

Furthermore, the contents of Si in the side margin portions 32, 34 ofthe multilayer ceramic capacitor 10 according to this preferredembodiment preferably is about 1.0 or more and about 7.0 or less in Simolar number/Ti molar number calculated. When the Si molar number/Timolar number is less than about 1.0, the side margin portions 32, 34 areinsufficiently sintered, thus increasing the porosity, and fail toachieve sufficient improvement in deflecting strength.

On the other hand, when the Si molar number/Ti molar number exceedsabout 7.0, Si excessively diffuses into the internal electrodes, thusresulting in over-sintering, and decreasing reliability such as aninsulation resistance value.

Furthermore, in the multilayer ceramic capacitor 10 according to thispreferred embodiment, the side margin portions 32, 34 preferably havedimensions of about 5 μm or more and about 40 μm or less in the widthdirection of the laminated body 12, for example.

When the side margin portions 32, 34 exceed about 40 μm make itimpossible to ensure required capacitance.

When the side margin portions 32, 34 are less than about 5 μm, the sidemargin portions 32, 34 are insufficiently sintered, thus failing toobtain the dense side margin portions 32, 34. When the side marginportions are not dense, water ingress from the outside is easily caused.

Subsequently, a non-limiting example of a method for manufacturing themultilayer ceramic capacitor will be described. FIGS. 9A and 9B arediagrams for explaining a non-limiting example of method formanufacturing the multilayer ceramic capacitor according to thispreferred embodiment, where FIG. 9A is a schematic view illustratingceramic green sheets with conductive films formed, and FIG. 9B is apattern diagram illustrating the stacked ceramic green sheets with theconductive films formed. FIG. 10 is a perspective view illustrating apreferred embodiment of the appearance of a laminated body chip obtainedby the method for manufacturing the multilayer ceramic capacitoraccording to this preferred embodiment.

First, a perovskite-type compound containing Ba and Ti is prepared as adielectric ceramic material. The dielectric powder obtained from thedielectric ceramic material is mixed with at least one of Si, Mg, and Baas an additive, as well as an organic binder, an organic solvent, aplasticizer, and a dispersant in a predetermined proportion, thuspreparing a ceramic slurry. The ceramic slurry is formed into ceramicgreen sheets 50 a and 50 b on the surfaces of multiple resin films (notshown). The ceramic green sheets 50 b are stacked alternately with theceramic green sheet 50 a, and the ceramic green sheets 50 a (50 b) areformed with the use of, for example, a die coater, a gravure coater, anda micro-gravure coater.

Next, as shown in FIG. 9A, onto the surfaces of the ceramic green sheets50 a (50 b), a conductive paste to form internal electrodes is appliedin the form of stripes in an X direction, and dried. It is to be notedthat the direction in which the conductive paste to form internalelectrodes extends in the form of stripes is hereinafter referred to asthe X direction. In addition, the width direction of conductive films 52a, 52 b is referred to as a Y direction. In this way, the conductivefilms 52 a (52 b) are formed to define and function as the firstinternal electrodes 22 (second internal electrodes 24). For the printingmethod, various types of methods can be used, such as screen printing,ink-jet printing, and gravure printing. The conductive films 52 a, 52 bpreferably are, for example, about 1.5 μm or less in thickness.

First, a predetermined number of ceramic green sheets with no conductivefilm formed is stacked, which defines and functions as the outer layerportion 28, and next, as shown in FIG. 9B, the multiple ceramic greensheets 50 a, 50 b with the conductive films 52 a, 52 b applied areshifted in the Y direction, and stacked to define and function as theinner layer portion 26. Furthermore, on the inner layer portion 26, apredetermined number of ceramic green sheets with no conductive filmformed is stacked, which defines and functions as the outer layerportion 30, thus providing a mother stacked body.

Next, the obtained mother stacked body is pressed. Methods such as rigidpressing and isostatic pressing can be used as the method for pressingthe mother stacked body.

Next, the pressed mother stacked body is cut into a chip shape, thusproviding a stacked body chip 60 as shown in FIG. 10. Various types ofmethods such as push-cutting, dicing, and laser can be used as themethod for cutting the mother stacked body.

As shown in FIG. 10, only the conductive films 52 a of the ceramic greensheets 50 a are exposed at one end surface of the stacked body chip 60obtained through the foregoing steps. In addition, only the conductivefilms 52 b of the ceramic green sheets 50 b are exposed at the other endsurface.

In addition, the conductive film 52 a of the ceramic green sheets 50 aand the conductive films 52 b of the ceramic green sheets 50 b areexposed respectively at both side surfaces of the stacked body chip 60.

Subsequently, the procedure will be described for preparing ceramicgreen sheets for side margins to define and function as the side marginportions 32, 34.

First, a perovskite-type compound containing Ba and Ti is prepared as adielectric ceramic material. The dielectric powder obtained from thedielectric ceramic material is mixed with at least one of Si, Mg, and Baas an additive, as well as a binder resin, an organic solvent, aplasticizer, and a dispersant in predetermined proportion, thuspreparing ceramic slurry.

In this regard, Si is added to the ceramic slurry to define and functionas the outer layer 32 a of the side margin portion 32 (and the outerlayer 34 a of the side margin portion 34). Specifically, Si is addedsuch that the Si mole number/Ti mole number is about 1.0 or more andabout 7.0 or less, for example. In addition, Si is also added to theceramic slurry to define and function as the inner layer 32 b of theside margin portion 32 (and the inner layer 34 b of the side marginportion 34). Specifically, Si is added such that the Si mole number/Timole number is about 1.0 or more and about 4.0 or less, for example.

In addition, Ba is added to the ceramic slurry to define and function asthe outer layer 32 a of the side margin portion 32 (and the outer layer34 a of the side margin portion 34). Specifically, Ba is added such thatthe Ba mole number/Ti mole number is about 0.00 or more and less thanabout 0.02, for example.

In addition, Ba is also added to the ceramic slurry to define andfunction as the inner layer 32 b of the side margin portion 32 (and theinner layer 34 b of the side margin portion 34). Specifically, Ba isadded such that the Ba mole number/Ti mole number is about 0.02 or moreand less than about 0.04, for example.

Furthermore, the amount of PVC that is polyvinyl chloride contained inthe ceramic slurry to define and function as the outer layers 32 a, 34 aof the side margin portions 32, 34 is higher than the amount ofpolyvinyl chloride (PVC) contained in the ceramic slurry to define andfunction as the inner layers 32 b, 34 b of the side margin portions 32,34.

Furthermore, as the solvent contained in the ceramic slurry to defineand function as the inner layers 32 b, 34 b of the side margin portions32, 34, an optimum solvent is selected appropriately to prevent thedissolution of the ceramic green sheets for outer layers. In addition,the ceramic green sheets for inner layers have a role for adhesion tothe stacked body chip 60.

Then, the prepared ceramic slurry to define and function as the outerlayers 32 a, 34 a is applied onto the surface of the resin films, anddried, thus providing ceramic green sheets for outer layers.

Next, the prepared ceramic slurry to define and function as the innerlayers 32 b, 34 b is applied onto the surface of the ceramic greensheets for outer layers, and dried, thus forming ceramic green sheetsfor inner layers. In the way described above, the ceramic green sheetsare obtained for side margins that have a two-layer structure.

In this regard, the dimension in the width direction of the ceramicgreen sheets for inner layers is preferably smaller than the dimensionin the width direction of the ceramic green sheets for outer layers.Specifically, for example, as for the thickness after firing, theceramic green sheets for outer layers preferably are formed to be about5 μm or more and about 20 μm or less, and the ceramic green sheets forinner layers preferably are formed to be about 0.1 μm or more and about20 μm or less.

It is to be noted that a case has been described above, where theceramic green sheets for side margins of two-layer structure areobtained by applying the ceramic green sheets for inner layers onto thesurfaces of the ceramic green sheets for outer layers, and drying thesheets. However, the present invention is not limited to this case,ceramic green sheets for outer layers and ceramic green sheets for innerlayers may be each formed in advance, and then bonded to each other,thus providing ceramic green sheets for side margins of two-layerstructure. It is to be noted that the ceramic green sheets for sidemargins are not limited to two layers, but may have three or moremultiple layers.

Next, the ceramic green sheets for side margins are peeled from theresin film.

Subsequently, the ceramic green sheet for inner layers from the peeledceramic green sheets for side margins is opposed to and pressed againstthe side surface of the stacked body chip at which the conductive films52 a, 52 b are exposed, and subjected to punching, thus forming a layerto define and function as the side margin portion 32. Furthermore, forthe side surface of the stacked body chip 60 on which a layer is notformed to define and function as the side margin portion 32, the ceramicgreen sheet for inner layers is opposed to and pressed against the sidesurface of the stacked body chip 60 at which the conductive films 52 a,52 b are exposed, and subjected to punching, thus forming a layer todefine and function as the side margin portion 34. In this case, it ispreferable to apply an organic solvent as an adhesive in advance to theside surfaces of the stacked body chip 60.

Next, the stacked body chip 60 with the layers formed to define andfunction as the side margin portions 32, 34 is subjected to a degreasingtreatment under a predetermined condition in a nitrogen atmosphere, andthen subjected to firing at a predetermined temperature in a mixedatmosphere of nitrogen-hydrogen-water vapor, thus providing the sinteredlaminated body 12.

Next, an external electrode paste containing Cu as its main constituentis applied to each of two end surfaces of the sintered laminated body12, and baked to form the base electrode 40 a connected to the firstinternal electrode 22 and the base electrode 42 a connected to thesecond internal electrodes. Furthermore, on the surfaces of the baseelectrode layers 40 a, 42 a, the lower layer platings 40 b, 42 b areformed by Ni plating, and on the surfaces of the lower layer platings 40b, 42 b, the upper layer platings 40 c, 42 c are formed by Sn plating,thus forming the first and second external electrodes 40, 42.

In the way described above, the multilayer ceramic capacitor 10 ismanufactured as shown in FIG. 1.

It is to be noted that the side margin portions 32, 34 may be formed byapplying ceramic slurry for side margins to the both side surfaces ofthe stacked body chip 60 at which the conductive films 52 a, 52 b areexposed.

More specifically, ceramic slurry to define and function as the innerlayers 32 b, 34 b is applied to the both side surfaces of the stackedbody chip 60 at which the conductive films 52 a, 52 b are exposed, anddried. Furthermore, ceramic slurry to define and function as the outerlayers 32 a, 34 a is applied to the surfaces of the inner layers 32 b,34 b.

In this case, the thickness for each ceramic slurry to define andfunction as the outer layers 32 a, 34 a and the inner layers 32 b, 34 bis able to be adjusted by changing the amount of the resin included ineach ceramic slurry.

In addition, the side margin portions 32, 34 may be formed by, with theboth end surfaces of the stacked body chip 60 masked with a resin or thelike, dipping the whole stacked body chip 60 in the ceramic slurry todefine and function as the inner layers 32 b, 34 b, drying the chip, andfurther dipping the chip in the ceramic slurry to define and function asthe outer layers 32 a, 34 a. In this case, the inner layers and theouter layers are formed on the outer layer portions 28, 30, thus formingthree-layer structures.

An experimental example will be described below. In the experimentalexample, respective samples of multilayer ceramic capacitors accordingto the following example and comparative example were produced, andevaluated by measuring the hardness at side margin portion surfaces ofthe multilayer ceramic capacitors with a Vickers hardness tester.

EXAMPLE

First, in the example, the sample of the multilayer ceramic capacitorshown in FIG. 1 was produced by the method mentioned above. In thiscase, the external dimensions of the multilayer ceramic capacitor weremade about 1.0 mm in length, about 0.5 mm in width, and about 0.5 mm inheight, for example. In the example, prepared was the multilayer ceramiccapacitor including side margin portions of two-layer structure composedof an inner layer containing Si at a Si mole number/Ti mole number ofabout 3.5 with respect to Ti and an outer layer containing Si at a Simole number/Ti mole number of about 5 with respect to Ti. In addition,the thickness of the side margin portion was made about 20 μm. It is tobe noted that for the side margin portion according to the example, thethickness of the outer layer was made about 16 μm, and the thickness ofthe inner layer was made about 4 μm.

COMPARATIVE EXAMPLE

In the comparative example, the multilayer ceramic capacitor wasproduced under the same conditions as in the example, except that sidemargin portions of one-layer structure containing Si at a Si molenumber/Ti mole number of 3.5 with respect to Ti were adopted without theside margin portions composed of the two layers of the inner layer andthe outer layer.

Evaluation Method

Five multilayer ceramic capacitors were prepared for each sample of themultilayer ceramic capacitors according to the example and comparativeexample described above, and the hardness of the side margin portionsurface was measured with a Vickers hardness tester at both sidesurfaces of the multilayer ceramic capacitors. The conditions for themeasurement of the Vickers hardness were the measurement weight: 200 gfand the holding time at a bottom dead point: 10 s. In addition, the porearea ratio in the vicinity of the side margin portion surface wascalculated for each sample of the multilayer ceramic capacitorsaccording to the example and the comparative example. For the pore arearatio, the surface including the side margin portion is exposed, and animage of the surface is taken with a SEM. The image taken is subjectedto image processing to measure the pore area. The pore area divided bythe area of the multilayer ceramic capacitor in the image taken iscalculated as the pore area ratio.

FIG. 11 is a diagram showing the relationship between the pore arearatio in the vicinity of the side margin portion surface and the Vickershardness at the side margin portion surface.

As a result of the experiment, as shown in FIG. 11, in the case of themultilayer ceramic capacitor according to the example of a preferredembodiment of the present invention, the pore area ratio was about 0.3%around the side margin portion surface, and the Vickers hardness wasabout 1470 MPa or more and 1680 MPa or less at the side margin portionsurface, for example.

On the other hand, as shown in FIG. 11, in the case of the multilayerceramic capacitor according to the comparative example, the pore arearatio was 1.9% around the side margin portion surface, and the Vickershardness was 1140 MPa or more and 1270 MPa or less at the side marginportion surface.

From the foregoing, it has been demonstrated that a multilayer ceramiccapacitor according to an example of a preferred embodiment of thepresent invention has deflecting strength improved more than themultilayer ceramic capacitor according to the comparative example.

It is to be noted that the present invention is not limited to thepreferred embodiments described above, but various modifications can bemade within the scope of the present invention.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A multilayer ceramic capacitor comprising: alaminated body including a plurality of dielectric layers and aplurality of internal electrodes; and a plurality of external electrodeselectrically connected to the plurality of internal electrodes; whereinthe laminated body includes a first principal surface and a secondprincipal surface opposed in a laminating direction, a first sidesurface and a second side surface opposed in a width directionperpendicular or substantially perpendicular to the laminatingdirection, and a first end surface and a second end surface opposed in alength direction perpendicular or substantially perpendicular to boththe laminating direction and the width direction; the plurality ofinternal electrodes includes first internal electrodes exposed at thefirst end surface, and second internal electrodes exposed at the secondend surface and opposed to the first internal electrodes with thedielectric layers interposed therebetween; the laminated body includesouter layer portions provided at a top and a bottom of the laminatedbody in the laminating direction, and an inner layer portion between theouter layer portions; the plurality of external electrodes includes afirst external electrode covering the first end surface and electricallyconnected to the first internal electrodes, and a second externalelectrode covering the second end surface and connected to the secondinternal electrodes; side margin portions that sandwich the inner layerportion and the outer layer portions in the width direction; the sidemargin portions include outer layers and inner layers, the outer layersbeing located closer to the first and second side surfaces than theinner layers, and the inner layers being located closer to the pluralityof internal electrodes than the outer layers; and dimensions of theouter layers in the width direction are larger than dimensions of theinner layers in the width direction.
 2. The multilayer ceramic capacitoraccording to claim 1, wherein a sinterability of the outer layers isdifferent from a sinterability of the inner layers.
 3. The multilayerceramic capacitor according to claim 1, wherein the dimensions of theouter layers in the width direction are about 5 μm or more and about 20μm or less.
 4. The multilayer ceramic capacitor according to claim 1,wherein the dimensions of the inner layers in the width direction areabout 0.1 μm or more and about 20 μm or less.
 5. The multilayer ceramiccapacitor according to claim 1, wherein a content of Si in the outerlayers is higher than a content of Si in the inner layers.
 6. Themultilayer ceramic capacitor according to claim 1, wherein the pluralityof external electrodes electrically connected to the internal electrodesare co-fired.
 7. The multilayer ceramic capacitor according to claim 1,wherein the plurality of dielectric layers have thicknesses of about 0.2um or more and about 10 um or less.
 8. The multilayer ceramic capacitoraccording to claim 1, wherein the plurality of inner electrodes havethicknesses of about 0.3 μm or more and about 2.0 μm or less.
 9. Themultilayer ceramic capacitor according to claim 1, wherein dimensions ofthe outer layer portions in the laminating direction are about 15 μm ormore.
 10. The multilayer ceramic capacitor according to claim 1, whereindimensions of the outer layer portions in the laminating direction areabout 40 μm or less.
 11. The multilayer ceramic capacitor according toclaim 1, wherein the outer layer portions are made of a same dielectricceramic material as the ceramic layers in the inner layer portion. 12.The multilayer ceramic capacitor according to claim 1, wherein the outerlayer portions are made of a material that is different from the ceramiclayers in the inner layer portion.